Electrophoretic apparatus and electronic equipment

ABSTRACT

A mixture of a first material having high chemical affinity for the electrophoretic particles  6   a  and a second material having low chemical affinity therefor is used as a binder for fixing microcapsules  5  between a first electrode  3  and a second electrode  4.

FIELD OF THE INVENTION

The present invention relates to an electrophoretic apparatus andelectronic equipment provided with the same.

BACKGROUND OF THE INVENTION

Electrophoretic display devices that take advantage of theelectrophoretic phenomenon are known as non-emissive display devices.The electrophoretic phenomenon refers to the phenomenon in which when anelectric field is applied to a suspension composed of a liquid phasedispersion medium with fine particles dispersed therein, the particles,which are naturally charged through dispersion (electrophoreticparticles), migrate due to a Coulomb force.

In a basic structure of the electrophoretic display device, oneelectrode and another electrode are facing each other with apredetermined spacing, and the above-described suspension(electrophoretic suspension) is enclosed therebetween. Furthermore, atleast one electrode is transparent, and this transparent electrode sideserves as an observation surface. When a potential difference is appliedbetween these two electrodes, electrophoretic particles are attracted toeither of the electrodes, depending on the direction of the electricfield.

Consequently, in this structure, when the dispersion medium is dyed witha dye and the electrophoretic particles are composed of pigmentparticles, either the color of the electrophoretic particles or thecolor of the dye can be observed, depending on the direction of theelectric field through the transparent observation surface. Therefore,an image can be displayed by forming the electrode with a pattern inaccordance with each pixel, and controlling a voltage applied to eachpixel electrode.

Such an electrophoretic display device is noted as an electro-opticalapparatus suitable for a new display because of the advantages of asimple configuration, a wide viewing angle range, a low powerconsumption, a display image holding performance (hereafter referred toas “memorization property”), and the like.

A microcapsule type electrophoretic display device is an example of anelectrophoretic display device (for example, refer to the followingPatent literature 1). In this device, a plurality of microcapsulescontaining an electrophoretic suspension are disposed between a pair ofelectrodes. In this device, a capsule film of each microcapsule iscomposed of, for example, a mixture of gelatin and gum Arabic. Thismicrocapsule is fixed between the electrodes with a binder made of asilicone resin, an acrylic resin, an urethane resin or the like. See,for example, Japanese Unexamined Patent Application Publication No.1-86116.

However, conventional electrophoretic display devices are susceptible toimprovement in the compatibility between the memorization property andthe erasability. That is, when the application of a voltage is stoppedafter an image is displayed by application of the voltage, the displayedimage disappears in a short time. On the other hand, when thememorization property is improved, erasure is not easily performed dueto phenomena such as image persistence, and rewrite of the displaybecomes difficult.

SUMMARY OF THE INVENTION

The present invention was made to overcome the above-described problemsin the conventional technology. Accordingly, it is an object of thepresent invention to provide a electrophoretic display device having anexcellent memorization property and excellent □ras ability.

In order to overcome the above-described problems, the present inventionprovides an electrophoretic apparatus (a first electrophoreticapparatus) including a first electrode, a second electrode and aplurality of closed spaces divided by partitions, wherein theabove-described closed space contains an electrophoretic suspension inwhich electrophoretic particles are dispersed in a dispersion medium,the above-described electrophoretic particles migrate by application ofa voltage via the above-described first electrode and theabove-described second electrode, a component is disposed between theabove-described closed space and at least one of the above-describedfirst electrode and the above-described second electrode, and theabove-described component is composed of a mixture including at leasttwo different materials of a first material and a second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the affinity of the above-described first material for theabove-described electrophoretic particles is higher than the affinity ofthe above-described second material for the above-describedelectrophoretic particles.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the above-described first material and the above-describedsecond material have different holding powers for holding the unevendistribution state of the above-described electrophoretic particleswithout applying any voltage, the uneven distribution state being causedby the application of a voltage, and the above-described holding powerof the above-described first material being higher than that of theabove-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the polarity of the above-described first material is higherthan the polarity of the above-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the above-described electrophoretic particles are titaniumdioxide (TiO₂) particles, the above-described first material is anacrylic resin, and the above-described second material is a siliconeresin.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the above-described electrophoretic particles are composed ofpositively charged particles and negatively charged particles which havecolors different from each other.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described first electrophoretic apparatus,wherein the above-described electrophoretic particles are composed oftitanium dioxide (TiO₂) particles and colored particles made of anacrylic resin, the above-described first material is an acrylic resin,and the above-described second material is a silicone resin.

The present invention also provides an electrophoretic apparatus (asecond electrophoretic apparatus) including a first electrode, a secondelectrode and a plurality of microcapsules, wherein the above-describedmicrocapsule contains an electrophoretic suspension in whichelectrophoretic particles are dispersed in a dispersion medium, theabove-described electrophoretic particles migrate by application of avoltage via the above-described first electrode and the above-describedsecond electrode, a component is disposed between the above-describedmicrocapsules and at least one of the above-described first electrodeand the above-described second electrode, and the above-describedcomponent is composed of a mixture including at least two differentmaterials of a first material and a second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the affinity of the above-described first material for theabove-described electrophoretic particles is higher than the affinity ofthe above-described second material for the above-describedelectrophoretic particles.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the first material and the second material have differentholding powers for holding the uneven distribution state of theabove-described electrophoretic particles without applying any voltage,the uneven distribution state being caused by the application of avoltage, and the above-described holding power of the above-describedfirst material is higher than that of the above-described secondmaterial.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the polarity of the above-described first material is higherthan the polarity of the above-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the above-described electrophoretic particles are titaniumdioxide (TiO₂) particles, the above-described first material is anacrylic resin, and the above-described second material is a siliconeresin.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the above-described electrophoretic particles are composed ofpositively charged particles and negatively charged particles which havecolors different from each other.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described second electrophoretic apparatus,wherein the above-described electrophoretic particles are composed oftitanium dioxide (TiO₂) particles and colored particles made of acrylicresin, the above-described first material is an acrylic resin, and theabove-described second material is a silicone resin.

The present invention also provides an electrophoretic apparatus (athird electrophoretic apparatus) including a first electrode, a secondelectrode and a plurality of closed spaces divided by partitions,wherein the above-described closed space contains an electrophoreticsuspension in which electrophoretic particles are dispersed in adispersion medium, the above-described electrophoretic particles migrateby application of a voltage via the above-described first electrode andthe above-described second electrode, a component is disposed betweenthe above-described closed space and at least one of the above-describedfirst electrode and the above-described second electrode, and theabove-described component is composed of at least a first component madeof a first material and a second component made of a second materialdifferent from the above-described first material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the affinity of the above-described first material for theabove-described electrophoretic particles is higher than the affinity ofthe above-described second material for the above-describedelectrophoretic particles.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described first material and the above-describedsecond material have different holding powers for holding the unevendistribution state of the above-described electrophoretic particleswithout applying any voltage, the uneven distribution state being causedby the application of a voltage, and the holding power of theabove-described first material is higher than that of theabove-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the polarity of the above-described first material is higherthan the polarity of the above-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described first component is disposed closer to atleast one of the above-described first electrode and the above-describedsecond electrode than is the above-described second component.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described first component is disposed in contact withat least one of the above-described first electrode and theabove-described second electrode.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described electrophoretic particles are titaniumdioxide (TiO₂) particles, the above-described first material is anacrylic resin, and the above-described second material is a siliconeresin.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described electrophoretic particles are composed ofpositively charged particles and negatively charged particles which havecolors different from each other.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described third electrophoretic apparatus,wherein the above-described electrophoretic particles are composed oftitanium dioxide (TiO₂) particles and colored particles made of anacrylic resin, the above-described first material is an acrylic resin,and the above-described second material is a silicone resin.

The present invention also provides an electrophoretic apparatus (afourth electrophoretic apparatus) including a first electrode, a secondelectrode and a plurality of microcapsules, wherein the above-describedmicrocapsule contains an electrophoretic suspension in whichelectrophoretic particles are dispersed in a dispersion medium, theabove-described electrophoretic particles migrate by application of avoltage via the above-described first electrode and the above-describedsecond electrode, a component is disposed between the above-describedmicrocapsules and at least one of the above-described first electrodeand the above-described second electrode, and the above-describedcomponent is composed of at least a first component made of a firstmaterial and a second component made of a second material different fromthe above-described first material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the affinity of the above-described first material for theabove-described electrophoretic particles is higher than the affinity ofthe above-described second material for the above-describedelectrophoretic particles.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described first material and the above-describedsecond material have different holding powers for holding the unevendistribution state of the above-described electrophoretic particleswithout applying any voltage, the uneven distribution state being causedby the application of a voltage, and the above-described holding powerof the above-described first material is higher than that of theabove-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the polarity of the above-described first material is higherthan the polarity of the above-described second material.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described first component is disposed closer to atleast one of the above-described first electrode and the above-describedsecond electrode than is the above-described second component.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described first component is disposed in contact withat least one of the above-described first electrode and theabove-described second electrode.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described electrophoretic particles are titaniumdioxide (TiO₂) particles, the above-described first material is anacrylic resin, and the above-described second material is a siliconeresin.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described electrophoretic particles are composed ofpositively charged particles and negatively charged particles which havecolors different from each other.

The present invention also provides an electrophoretic apparatuscorresponding to the above-described fourth electrophoretic apparatus,wherein the above-described electrophoretic particles are composed oftitanium dioxide (TiO₂) particles and colored particles made of acrylicresin, the above-described first material is an acrylic resin, and theabove-described second material is a silicone resin.

Examples of the above-described first material (the materialconstituting the component composed of the above-described mixture inthe above-described first and second electrophoretic apparatuses, andthe material constituting the above-described first component in thethird and fourth electrophoretic apparatuses) include, for example,polyitaconic acid resins, polyvinyl alcohol resins, poly-n-vinylpyrrolidone resins, polyamide resins, polyurethane resins and acrylicresins. Examples of acrylic resins include, for example,poly-2-ethylhexyl acrylate, polyhydroxyethyl acrylate, polyhydroxypropylmethacrylate, polypropylene glycol acrylate, polyacrylamide andpolymethacrylamide.

Examples of the above-described second material (the materialconstituting the component composed of the above-described mixture inthe above-described first and second electrophoretic apparatuses, andthe material constituting the above-described second component in thethird and fourth electrophoretic apparatuses) include, for example,stearyl methacrylate-acrylonitrile resins, chromium complex resins,polyethylene resins and silicone resins. A fluorine-based compound maybe contained as an additive.

A preferable example of combinations of the electrophoretic particle,the first material and the second material is a combination in which theelectrophoretic particle is titanium dioxide (TiO₂), the first materialis an acrylic resin and the second material is a silicone resin. When anelectrophoretic suspension of two-particle type is used (when theelectrophoretic particles are composed of positively charged particlesand negatively charged particles which have colors different from eachother), a combination in which the electrophoretic particles aretitanium dioxide (TiO₂) particles and colored particles made of anacrylic resin, the first material is an acrylic resin and the secondmaterial is a silicone resin is preferable.

Examples of combinations of the first material and the second materialinclude a combination of a material having large surface energy and amaterial having small surface energy. Examples of materials having largesurface energy include poly-2-ethylhexyl acrylate, polyacrylic acid,polymethacrylic acid, polyitaconic acid, polyhydroxyethyl acrylate,polyhydroxypropyl methacrylate, polypropylene glycol acrylate,polyacrylamide, polymethacrylamide, polyvinyl alcohol, poly-N-vinylpyrrolidone and the like.

Examples of materials having small surface energy include siliconeresins, stearyl methacrylate-acrylonitrile resins, chromium complexresins and the like.

The present invention provides electronic equipment including theabove-described first to fourth electrophoretic apparatuses.

According to the present invention, a microcapsule type electrophoreticdisplay device having an excellent memorization property and excellenteras ability and electronic equipment including the same are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the first embodiment of the presentinvention

FIG. 2 is a diagram for explaining the displaying method by theelectrophoretic display device of the first embodiment;

FIG. 3 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the second embodiment of the presentinvention;

FIG. 4 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the third embodiment of the presentinvention;

FIG. 5 is a diagram for explaining the displaying method by theelectrophoretic display device of the third embodiment;

FIG. 6 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the fourth embodiment of the presentinvention;

FIG. 7 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the fifth embodiment of the presentinvention;

FIG. 8 is a diagram for explaining the displaying method by theelectrophoretic display device of the fifth embodiment;

FIG. 9 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the sixth embodiment of the presentinvention;

FIG. 10 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the seventh embodiment of the presentinvention;

FIG. 11 is a diagram for explaining the displaying method by theelectrophoretic display device of the seventh embodiment;

FIG. 12 is a sectional view of one pixel showing the electrophoreticdisplay panel corresponding to the eighth embodiment of the presentinvention;

FIG. 13 is a diagram showing the manufacturing process of themicrocapsules adopted in the examples;

FIG. 14 is a perspective view showing the exterior configuration of theelectronic paper as an example of the electronic equipment of thepresent invention;

FIG. 15 is a sectional view (a) and a plan view (b) showing therewriting/display device of the electronic paper as an example of theelectronic equipment of the present invention;

FIG. 16 is a perspective view showing the exterior configuration of theelectronic note as an example of the electronic equipment of the presentinvention;

FIG. 17 is a perspective view showing the exterior configuration of theelectronic book as an example of the electronic equipment of the presentinvention;

FIG. 18 is a perspective view showing the exterior configuration of themobile type personal computer as an example of the electronic equipmentof the present invention;

FIG. 19 is a perspective view showing the exterior configuration of acellular phone as an example of the electronic equipment of the presentinvention; and

FIG. 20 is a perspective view showing the configuration of the digitalstill camera as an example of the electronic equipment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of ElectrophoreticApparatus

The electrophoretic display device, which is an embodiment of theelectrophoretic apparatus of the present invention, will be describedbelow.

An electrophoretic display device of the present embodiment is providedwith an electrophoretic display panel and a driving circuit. Theelectrophoretic display panel of the present embodiment will bedescribed with reference to FIG. 1. This drawing is a sectional view ofone pixel of the electrophoretic display panel.

This electrophoretic display panel (hereafter abbreviated as “panel”) iscomposed of a first substrate 1 and a second substrate 2 arranged toface each other, a first electrode 3 and a second electrode 4 fixed toopposing surfaces of the respective substrates 1 and 2, microcapsules 5arranged between the two electrodes 3 and 4, an electrophoreticsuspension 6 contained in the microcapsules 5, and a binder 7 for fixingthe microcapsules 5 between the two electrodes 3 and 4.

This panel is designed to be observed from the first substrate 1 side. Atransparent glass substrate is used as the first substrate, and apatterned ITO (Indium Tin Oxide: In₂O₃—SnO₂) thin film is used as thefirst electrode (an electrode formed from a transparent material:transparent electrode) 3. A glass substrate is used as the secondsubstrate 2, and a patterned aluminum (Al) thin film is used as thesecond electrode 4. The microcapsule 5 is formed from a mixture of gumArabic and gelatin.

The electrophoretic suspension 6 is composed of electrophoreticparticles 6 a, made of titanium dioxide particles, and a liquid phasedispersion medium 6 b, made of dodecylbenzene, colored by ananthraquinone-based blue dye. The titanium dioxide particles are whiteparticles and are positively charged while being dispersed indodecylbenzene.

The binder 7 is composed of a mixture of an acryl resin and a siliconeresin. This binder 7 corresponds to the “component” constituting thesecond electrophoretic apparatus of the present invention.

A display method of the electrophoretic display device of the presentembodiment will now be described with reference to FIG. 2. As shown inFIG. 2, this electrophoretic display device is composed of the panel 10shown in FIG. 1 and a driving circuit 20. The driving circuit 20 isprovided with a switch 21 and voltage sources 22 a and 22 b. The firstelectrode 3 of the panel 10 is connected to the switch 21, and thesecond electrode 4 is connected to one terminal of each of the voltagesources 22 a and 22 b.

As shown in FIG. 2(A), when the switch 21 is in an open position and novoltage is applied between the electrodes 3 and 4, the electrophoreticparticles 6 a in the microcapsule 5 are adjacent the second electrode 4side (lower position in the drawing) in accordance with gravity.Consequently, the blue liquid phase dispersion medium 6 b is observedfrom the first substrate (transparent substrate) 1 side. That is, thepixel becomes blue in this condition.

Now, as shown in FIG. 2(B), the switch 21 is connected to the voltagesource 22 a such that the second electrode 4 becomes positive and thefirst electrode 3 becomes negative and, thereby, positively chargedelectrophoretic particles 6 a migrate toward the first electrode(transparent electrode) 3 side because the first electrode 3 has becomea negative pole. Consequently, the white electrophoretic particles 6 aare observed from the first substrate (transparent substrate) 1 side.That is, the pixel becomes white in this condition.

Now, as shown in FIG. 2(C), the switch 21 is in the open position and,thereby, no voltage is applied between the electrodes 3 and 4. However,the electrophoretic particles 6 a remain adjacent the first electrode(transparent electrode) 3 side due to a Coulomb force between thenegative charge carried by the first electrode (transparent electrode) 3and the positive charge carried by the electrophoretic particles 6 a.Consequently, the white electrophoretic particles 6 a are still observedfrom the first substrate (transparent substrate) 1 side and, therefore,the pixel remains white.

Now, as shown in FIG. 2(D), the switch 21 is connected to the voltagesource 22 b such that the first electrode 3 becomes positive and thesecond electrode 4 becomes negative and, thereby, positively chargedelectrophoretic particles 6 a migrate toward the second electrode 4 sidebecause the second electrode 4 has become a negative pole. Consequently,the blue liquid phase dispersion medium 6 b is observed from the firstsubstrate (transparent substrate) 1 side. That is, the pixel becomesblue in this condition.

According to the electrophoretic display device of the presentembodiment, since a mixture of an acrylic resin that has a high chemicalaffinity for the electrophoretic particles 6 a is made of titaniumdioxide, and a silicone resin that has a low chemical affinity for theelectrophoretic particles 6 a is used as the binder 7, theelectrophoretic particles 6 a can be held adjacent the first electrode 3side for, for example, one month or more in the condition shown in FIG.2(C). When the switch 21 is changed from the condition shown in FIG.2(C) to the condition shown in FIG. 2(D), the electrophoretic particles6 a instantaneously move to the second electrode 4 side.

Therefore, according to the electrophoretic display device of thepresent embodiment, when the application of a voltage is stopped afteran image is displayed by application of the voltage, the displayed imagecan be held for a long time without disappearance. In addition, erasureof the image can be excellently performed immediately after theswitching takes place. That is, the electrophoretic display device ofthe present embodiment is a microcapsule type electrophoretic apparatusthat has an excellent memorization property and an excellenterasability.

In contrast, with respect to the panel 10 in which a silicone resin isused as the binder 7, although the electrophoretic particles 6 ainstantaneously move to the second electrode 4 side when the switch 21is changed from the condition shown in FIG. 2(C) to the condition shownin FIG. 2(D), the electrophoretic particles 6 a can be held adjacent thefirst electrode 3 side only for about 10 minutes in the condition shownin FIG. 2(C).

With respect to the panel 10 in which an acrylic resin is used as thebinder 7, although the electrophoretic particles 6 a can be heldadjacent the first electrode 3 side for, for example, six months or morein the condition shown in FIG. 2(C), when the switch 21 is changed fromthe condition shown in FIG. 2(C) to the condition shown in FIG. 2(D),all of the electrophoretic particles 6 a do not instantaneously move tothe second electrode 4 side in unison and, therefore, it may be observedthat white spots remain on a blue background in the resulting state.

An electrophoretic display device of the second embodiment will now bedescribed with reference to FIG. 3. The electrophoretic display deviceof the present embodiment is a partition type electrophoretic displaydevice. FIG. 3 is a sectional view of one pixel of an electrophoreticdisplay panel.

Since the electrophoretic display device of the present embodiment is apartition type, in contrast to the electrophoretic display device of themicrocapsule type in the first embodiment, an electrophoretic suspension6 that is composed of electrophoretic particles 6 a and a liquid phasedispersion medium 6 b is contained in a space divided by the partitions8, between the first and second electrodes 3 and 4. Other than thisdifference, the configuration is basically the same as that in the firstembodiment. That is, this electrophoretic display panel (hereafterabbreviated as “panel”) is provided with a first substrate 1 and asecond substrate 2 that are arranged to face each other, and a firstelectrode 3 and a second electrode 4 that are fixed to opposing surfacesof the respective substrates 1 and 2.

In this electrophoretic display device, a binder 7 composed of a mixtureof an acrylic resin and a silicone resin is provided between a layercomposed of the electrophoretic suspension 6 and the first electrode(transparent electrode) 3. This binder 7 corresponds to the “component”constituting the first electrophoretic apparatus of the presentinvention.

In this device as well, the electrophoretic suspension 6 is composed ofelectrophoretic particles 6 a made of titanium dioxide particles and aliquid phase dispersion medium 6 b made of dodecylbenzene colored by ananthraquinone-based blue dye. The titanium dioxide particles are whiteparticles and are positively charged while dispersed in dodecylbenzene.

In this device, the first electrode 3 on the observation surface side isconnected to one terminal of each of the voltage sources 22 a and 22 b,and the second electrode 4 is connected to the switch 21. In a mannersimilar to that in the first embodiment, when the switch 21 is operatedthe electrophoretic particles 6 a can be moved to the first electrode 3side or the second electrode 4 side and, thereby, each pixel can be madewhite or blue.

According to the electrophoretic display device of the presentembodiment, since a mixture of an acrylic resin that has a high chemicalaffinity for the electrophoretic particles 6 a made of titanium dioxide,and a silicone resin that has a low chemical affinity for theelectrophoretic particles 6 a is used as the binder 7, when theapplication of a voltage is stopped after an image is displayed byapplication of the voltage, the displayed image can be held for a longtime without disappearance. In addition, erasure of the image can beexcellently performed immediately after the switching takes place. Thatis, the electrophoretic display device of the present embodiment is amicrocapsule type electrophoretic apparatus having an excellentmemorization property and an excellent erasability.

An electrophoretic display device of the present embodiment is providedwith an electrophoretic display panel and a driving circuit. Theelectrophoretic display panel of the present embodiment will bedescribed with reference to FIG. 4. This drawing is a sectional view ofone pixel of the electrophoretic display panel.

This electrophoretic display panel (hereafter abbreviated as “panel”) iscomposed of a first substrate 1 and a second substrate 2 arranged toface each other, a first electrode 3 and a second electrode 4 fixed toopposing surfaces of the respective substrates 1 and 2, microcapsules 5arranged between the two electrodes 3 and 4, an electrophoreticsuspension 60 contained in the microcapsules 5, and a binder 7 forfixing the microcapsules 5 between the two electrodes 3 and 4.

This panel is designed to be observed from the first substrate 1 side. Atransparent glass substrate is used as the first substrate 1, and apatterned ITO (Indium Tin Oxide: In₂O₃—SnO₂) thin film is used as thefirst electrode (an electrode formed from a transparent material:transparent electrode) 3. A glass substrate is used as the secondsubstrate 2, and a patterned aluminum (Al) thin film is used as thesecond electrode 4.

The microcapsule 5 is formed from a mixture of gum Arabic and gelatin.

The electrophoretic suspension 60 is composed of white electrophoreticparticles 61 made of titanium dioxide particles, black electrophoreticparticles 62 made of acrylic resin particles, and a transparent liquidphase dispersion medium 63 made of dodecylbenzene. That is,electrophoretic particles composed of positively charged particles(acrylic resin particles) and negatively charged particles (titaniumdioxide particles), which have colors different from each other, areused in the present embodiment. The binder 7 is composed of a mixture ofan acryl resin and a silicone resin. This binder 7 corresponds to the“component” constituting the second electrophoretic apparatus of thepresent invention.

A display method of the electrophoretic display device of the presentembodiment will be described with reference to FIG. 5. As shown in FIG.5, this electrophoretic display device is composed of the panel 10Ashown in FIG. 4 and a driving circuit 20. The driving circuit 20 isprovided with a switch 21 and voltage sources 22 a and 22 b. The firstelectrode 3 of the panel 10A is connected to the switch 21, and thesecond electrode 4 is connected to one terminal of each of the voltagesources 22 a and 22 b.

As shown in FIG. 5(A), when the switch 21 is in an open position and novoltage is applied between the electrodes 3 and 4, the electrophoreticparticles 61 and 62 in the microcapsule 5 are uniformly dispersed in theliquid phase dispersion medium 63. Consequently, the liquid phasedispersion medium 63, in a condition in which electrophoretic particles61 and 62 are uniformly dispersed, is observed from the first substrate(transparent substrate) 1 side. That is, this pixel becomes transparent(in a strict sense, light gray) in this condition.

Now, as shown in FIG. 5(B), the switch 21 is connected to the voltagesource 22 a such that the second electrode 4 becomes positive and thefirst electrode 3 becomes negative and, thereby, the positively chargedblack electrophoretic particles 62 migrate toward the first electrode(transparent electrode) 3 side because the first electrode 3 has becomea negative pole. The negatively charged white electrophoretic particles61 migrate toward the second electrode 4 side because the secondelectrode 4 has become a positive pole. Consequently, the blackelectrophoretic particles 62 are observed from the first substrate(transparent substrate) 1 side. That is, this pixel becomes black inthis condition.

Following this condition, as shown in FIG. 5(C), the switch 21 isswitched to be in the open position and, thereby, no voltage is appliedbetween the electrodes 3 and 4. However, the electrophoretic particles62 remain adjacent the first electrode (transparent electrode) 3 sidedue to a Coulomb force between the negative charge carried by the firstelectrode (transparent electrode) 3 and the positive charge carried bythe electrophoretic particles 62. The electrophoretic particles 61remain adjacent the second electrode 4 side due to a Coulomb forcebetween the positive charge carried by the second electrode 4 and thenegative charge carried by the electrophoretic particles 61.Consequently, the black electrophoretic particles 62 are still observedfrom the first substrate (transparent substrate) 1 side and, therefore,this pixel remains black.

Now, as shown in FIG. 5(D), the switch 21 is connected to the voltagesource 22 b such that the first electrode 3 becomes positive and thesecond electrode 4 becomes negative and, thereby, the positively chargedblack electrophoretic particles 62 migrate toward the second electrode 4side because the second electrode 4 has become a negative pole. Thenegatively charged white electrophoretic particles 61 migrate toward thefirst electrode (transparent electrode) 3 side because the firstelectrode 3 has become a positive pole. Consequently, the whiteelectrophoretic particles 61 are observed from the first substrate(transparent substrate) 1 side. That is, this pixel becomes white inthis condition.

Since a mixture of an acrylic resin that has a high chemical affinityfor the electrophoretic particles 61, made of titanium dioxide, and theelectrophoretic particles 62, made of an acrylic resin, and a siliconeresin that has a low chemical affinity for the electrophoretic particles61 is used as the binder 7, the electrophoretic particles 62 can beadjacent the first electrode 3 side and the electrophoretic particles 61can be adjacent the second electrode 4 side for, for example, one monthor more in the condition shown in FIG. 5(C). When the switch 21 ischanged from the condition shown in FIG. 5(C) to the condition shown inFIG. 5(D), however, the electrophoretic particles 62 instantaneouslymove to the second electrode 4 side and the electrophoretic particles 61instantaneously move to the first electrode 3 side, in unison.

As such, when the application of a voltage is stopped after an image isdisplayed, the displayed image can be held for a long time without itdisappearing. In addition, erasure of the image can be excellentlyperformed immediately after the switching takes place. That is, theelectrophoretic display device of the present embodiment is amicrocapsule type electrophoretic apparatus having an excellentmemorization property and an excellent erasability.

In contrast, with respect to the panel 10A in which a silicone resin isused as the binder 7, although the electrophoretic particles 62instantaneously move to the second electrode 4 side and theelectrophoretic particles 61 instantaneously move to the first electrode3 side when the switch 21 is changed from the condition shown in FIG.5(C) to the condition shown in FIG. 5(D), the electrophoretic particles62 can be adjacent the first electrode 3 side and the electrophoreticparticles 61 can be adjacent the second electrode 4 side only for about10 minutes, in the condition shown in FIG. 5(C).

With respect to the panel 10A in which an acrylic resin is used as thebinder 7, although the electrophoretic particles 62 can be adjacent thefirst electrode 3 side and the electrophoretic particles 61 can beadjacent the second electrode 4 side for, for example, six months ormore in the condition shown in FIG. 5(C), when the switch 21 is changedfrom the condition shown in FIG. 5(C) to the condition shown in FIG.5(D), all of the electrophoretic particles 62 do not instantaneouslymove to the second electrode 4 side in unison and all of theelectrophoretic particles 61 do not instantaneously move to the firstelectrode 3 side in unison and, therefore, it may be observed that whitespots remain in a black background in the resulting state.

An electrophoretic display device of the fourth embodiment will now bedescribed with reference to FIG. 6. The electrophoretic display deviceof the present embodiment is a partition type electrophoretic displaydevice. FIG. 6 is a sectional view of one pixel of an electrophoreticdisplay panel.

Since the electrophoretic display device of the present embodiment is apartition type, in contrast to the electrophoretic display device of themicrocapsule type in the third embodiment, an electrophoretic suspension60 composed of electrophoretic particles 61 and 62 and a liquid phasedispersion medium 63 is contained in a space divided by partitions 8between the first and second electrodes 3 and 4. The configuration,other than this difference, is basically the same as that in the thirdembodiment. That is, this electrophoretic display panel (hereafterabbreviated as “panel”) is provided with a first substrate 1 and asecond substrate 2 arranged to face each other, and a first electrode 3and a second electrode 4 fixed to opposing surfaces of the respectivesubstrates 1 and 2.

In this electrophoretic display device, a binder 7 composed of a mixtureof an acrylic resin, and a silicone resin is provided between a layercomposed of the electrophoretic suspension 60 and the first electrode(transparent electrode) 3. This binder 7 corresponds to the “component”constituting the first electrophoretic apparatus of the presentinvention.

In this device as well, the electrophoretic suspension 60 is composed ofwhite electrophoretic particles 61 made of titanium dioxide particles,black electrophoretic particles 62 made of acrylic resin particles, anda transparent liquid phase dispersion medium 63 made of dodecylbenzene.That is, electrophoretic particles composed of positively chargedparticles (acrylic resin particles) and negatively charged particles(titanium dioxide particles), which have colors different from eachother, are used in the present embodiment.

In this device, the first electrode 3 on the observation surface side isconnected to one terminal of each of the voltage sources 22 a and 22 b,and the second electrode 4 is connected to the switch 21. In a mannersimilar to that in the first embodiment, the switch 21 is operated, theelectrophoretic particles 61 are moved to the first electrode 3 side orthe second electrode 4 side, and each pixel can be made white or black.

According to the electrophoretic display device of the presentembodiment, since a mixture of an acrylic resin that has a high chemicalaffinity for the electrophoretic particles 61 made of titanium dioxide,and the electrophoretic particles 62 is made of an acrylic resin and asilicone resin that has a low chemical affinity therefor is used as thebinder 7, when the application of a voltage is stopped after an image isdisplayed by application of the voltage, the displayed image can be heldfor a long time without disappearing. In addition, erasure of the imagecan be excellently performed immediately after the switching takesplace. That is, the electrophoretic display device of the presentembodiment is a microcapsule type electrophoretic apparatus having anexcellent memorization property and an excellent erasability.

An electrophoretic display device of the fifth embodiment is providedwith an electrophoretic display panel and a driving circuit. Theelectrophoretic display panel of the present embodiment will bedescribed with reference to FIG. 7. This drawing is a sectional view ofone pixel of the electrophoretic display panel.

This electrophoretic display panel (hereafter abbreviated as “panel”) iscomposed of a first substrate 1 and a second substrate 2 arranged toface each other, a first electrode 3 and a second electrode 4 fixed toopposing surfaces of the respective substrates 1 and 2, microcapsules 5arranged between the two electrodes 3 and 4, an electrophoreticsuspension 6 contained in the microcapsules 5, and first and secondbinders 71 and 72 for fixing the microcapsules 5 between the twoelectrodes 3 and 4.

This panel is designed to be observed from the first substrate 1 side. Atransparent glass substrate is used as the first substrate 1, and apatterned ITO (Indium Tin Oxide: In₂O₃—SnO₂) thin film is used as thefirst electrode (an electrode formed from a transparent material:transparent electrode) 3. A glass substrate is used as the secondsubstrate 2, and a patterned aluminum (Al) thin film is used as thesecond electrode 4. The microcapsule 5 is formed from a mixture of gumArabic and gelatin.

The electrophoretic suspension 6 is composed of electrophoreticparticles 6 a, made of titanium dioxide particles, and a liquid phasedispersion medium 6 b, made of dodecylbenzene, colored by ananthraquinone-based blue dye. The titanium dioxide particles are whiteparticles and are positively charged while being dispersed indodecylbenzene.

The first binder 71 is made of an acrylic resin and is formed into alaminar shape all over the surface (the surface opposite to the firstsubstrate 1 side) of the first electrode 3. The second binder 72 is madeof a silicone resin and is disposed to fill in the space enclosed by thesecond electrode 4, the layer made of the first binder 71, and themicrocapsules 5 in one pixel. That is, in the laminar material, aplurality of microcapsules 5 are arranged such that one microcapsule isdisposed in the thickness direction, and are fixed with the secondbinder 72. The laminar material is fixed to the first electrode 3 withthe first binder 71, and is fixed to the second electrode 4 with thesecond binder 72.

This first binder 71 corresponds to the “first component” constitutingthe fourth electrophoretic apparatus of the present invention, and thesecond binder 72 corresponds to the “second component” constituting thefourth electrophoretic apparatus of the present invention.

A display method of the electrophoretic display device of the presentembodiment will now be described with reference to FIG. 8. As shown inFIG. 8, this electrophoretic display device is composed of the panel 10Bshown in FIG. 8 and a driving circuit 20. The driving circuit 20 isprovided with a switch 21 and voltage sources 22 a and 22 b. The firstelectrode 3 of the panel 10B is connected to the switch 21, and thesecond electrode 4 is connected to one terminal of each of the voltagesources 22 a and 22 b.

As shown in FIG. 8(A), when the switch 21 is in the open position, andno voltage is applied between the electrodes 3 and 4, theelectrophoretic particles 6 a in the microcapsule 5 are adjacent thesecond electrode 4 side (lower position in the drawing) in accordancewith gravity. Consequently, the blue liquid phase dispersion medium 6 bis observed from the first substrate (transparent substrate) 1 side.That is, the pixel becomes blue in this condition.

Now, as shown in FIG. 8(B), the switch 21 is connected to the voltagesource 22 a in order that the second electrode 4 becomes positive andthe first electrode 3 becomes negative and, thereby, positively chargedelectrophoretic particles 6 a migrate toward the first electrode(transparent electrode) 3 side, because the first electrode 3 has becomea negative pole. Consequently, the white electrophoretic particles 6 aare observed from the first substrate (transparent substrate) 1 side.That is, this pixel becomes white in this condition.

Following this condition, as shown in FIG. 8(C), the switch 21 is in theopen position and, thereby, no voltage is applied between the electrodes3 and 4 in the resulting condition. However, the electrophoreticparticles 6 a remain adjacent the first electrode (transparentelectrode) 3 side due to a Coulomb force between the negative chargecarried by the first electrode (transparent electrode) 3 and thepositive charge carried by the electrophoretic particles 6 a.Consequently, the white electrophoretic particles 6 a are still observedfrom the first substrate (transparent substrate) 1 side and, therefore,this pixel remains white.

Now, as shown in FIG. 8(D), the switch 21 is connected to the voltagesource 22 b such that the first electrode 3 becomes positive and thesecond electrode 4 becomes negative and, thereby, the positively chargedelectrophoretic particles 6 a migrate toward the second electrode 4 sidebecause the second electrode 4 has become a negative pole. Consequently,the blue liquid phase dispersion medium 6 b is observed from the firstsubstrate (transparent substrate) 1 side. That is, this pixel becomesblue in this condition.

Since the first binder 71 is made of an acrylic resin that has a highchemical affinity for the electrophoretic particles 6 a made of titaniumdioxide and is formed into a laminar shape on the first electrode 3, andthe second binder 72 is made of a silicone resin that has a low chemicalaffinity therefor is used to fix between microcapsules 5 adjacent toeach other, the electrophoretic particles 6 a can be held in the firstelectrode 3 side for, for example, one month or more in the conditionshown in FIG. 8(C). When the switch 21 is changed from the conditionshown in FIG. 8(C) to the condition shown in FIG. 8(D), theelectrophoretic particles 6 a instantaneously move to the secondelectrode 4 side, in unison.

As such, when the application of a voltage is stopped after an image isdisplayed by application of the voltage, the displayed image can be heldfor a long time without disappearing. In addition, erasure of the imagecan be excellently performed immediately after the switching takesplace. That is, the electrophoretic display device of the presentembodiment is a microcapsule type electrophoretic apparatus having anexcellent memorization property and an excellent erasability.

In contrast, with respect to a panel which differs simply in that thereis no layer made of the first binder 71 is disposed therein, althoughthe electrophoretic particles 6 a instantaneously move to the secondelectrode 4 side when the switch 21 is changed from the condition shownin FIG. 8(C) to the condition shown in FIG. 8(D), the electrophoreticparticles 6 a can be adjacent the first electrode 3 side only for about10 minutes in the condition shown in FIG. 8(C).

With respect to a panel in which no layer made of the first binder 71 isdisposed therein, and an acrylic resin is used as the second binder 72,although the electrophoretic particles 6 a can be adjacent the firstelectrode 3 side for, for example, six months or more in the conditionshown in FIG. 8(C), when the switch 21 is changed from the conditionshown in FIG. 8(C) to the condition shown in FIG. 8(D), all of theelectrophoretic particles 6 a do not instantaneously move to the secondelectrode 4 side in unison and, therefore, it may be observed that whitespots remain in a blue background.

An electrophoretic display device of the sixth embodiment will now bedescribed with reference to FIG. 9. The electrophoretic display deviceof the present embodiment is a partition type electrophoretic displaydevice. FIG. 9 is a sectional view of one pixel of an electrophoreticdisplay panel.

Since the electrophoretic display device of the present embodiment is apartition type, in contrast to the electrophoretic display device of themicrocapsule type in the fifth embodiment, an electrophoretic suspension6 composed of electrophoretic particles 6 a and a liquid phasedispersion medium 6 b is contained in the space divided by thepartitions 8 between the first and second electrodes 3 and 4. Theconfiguration, other than this difference, is basically the same as thatin the fifth embodiment. That is, this electrophoretic display panel(hereafter abbreviated as “panel”) is provided with a first substrate 1and a second substrate 2 arranged to face each other, and a firstelectrode 3 and a second electrode 4 are fixed to opposing surfaces ofthe respective substrates 1 and 2.

In this electrophoretic display device, a first layer 71 a, made of anacrylic resin, and a second layer 72 a, made of a silicone resin, areprovided between the layer made of the electrophoretic suspension 6 andthe first electrode (transparent electrode) 3, in that order, from thefirst electrode 3 side. This first layer 71 a corresponds to the “firstcomponent” constituting the third electrophoretic apparatus of thepresent invention, and the second layer 72 a corresponds to the “secondcomponent” constituting the fourth electrophoretic apparatus of thepresent invention.

In this device as well, the electrophoretic suspension 6 is composed ofelectrophoretic particles 6 a, made of titanium dioxide particles, and aliquid phase dispersion medium 6 b, made of dodecylbenzene, colored byan anthraquinone-based blue dye. The titanium dioxide particles arewhite particles and are positively charged while being dispersed indodecylbenzene.

In this device, the first electrode 3 on the observation surface side isconnected to one terminal of each of the voltage sources 22 a and 22 b,and the second electrode 4 is connected to the switch 21. In a mannersimilar to that in the first embodiment, the switch 21 is operated, theelectrophoretic particles 6 a are moved to the first electrode 3 side orthe second electrode 4 side, and each pixel can be made white or blue.

Since the first layer 71 is made of an acrylic resin that has a highchemical affinity for the electrophoretic particles 6 a made of titaniumdioxide, and the second layer 72 made of a silicone resin has a lowchemical affinity therefor are provided between the layer made of theelectrophoretic suspension 6 and the first electrode (transparentelectrode) 3, in that order, from the first electrode 3 side, when theapplication of a voltage is stopped after an image is displayed byapplication of the voltage, the displayed image can be held for a longtime without disappearing. In addition, erasure of the image can beexcellently performed immediately after the switching takes place. Thatis, the electrophoretic display device of the present embodiment is amicrocapsule type electrophoretic apparatus having an excellentmemorization property and an excellent erasability.

An electrophoretic display device of the seventh embodiment is providedwith an electrophoretic display panel and a driving circuit. Theelectrophoretic display panel of the present embodiment will bedescribed with reference to FIG. 10. This drawing is a sectional view ofone pixel of the electrophoretic display panel.

This electrophoretic display panel (hereafter abbreviated as “panel”) iscomposed of a first substrate 1 and a second substrate 2 arranged toface each other, a first electrode 3 and a second electrode 4 fixed toopposing surfaces of the respective substrates 1 and 2, microcapsules 5arranged between the two electrodes 3 and 4, electrophoretic suspensions60 contained in the microcapsules 5, and first and second binders 71 and72 for fixing the microcapsules 5 between the two electrodes 3 and 4.

This panel is designed to be observed from the first substrate 1 side. Atransparent glass substrate is used as the first substrate 1, and apatterned ITO (Indium Tin Oxide: In₂O₃—SnO₂) thin film is used as thefirst electrode (an electrode formed from a transparent material:transparent electrode) 3. A glass substrate is used as the secondsubstrate 2, and a patterned aluminum (Al) thin film is used as thesecond electrode 4. The microcapsule 5 is formed from a mixture of gumArabic and gelatin.

The electrophoretic suspension 60 is composed of white electrophoreticparticles 61 made of titanium dioxide particles, black electrophoreticparticles 62 made of acrylic resin particles and a transparent liquidphase dispersion medium 63 made of dodecylbenzene. That is,electrophoretic particles composed of positively charged particles(acrylic resin particles) and negatively charged particles (titaniumdioxide particles) which have colors different from each other are usedin the present embodiment.

The first binder 71 is made of an acrylic resin, and is formed into alaminar shape all over the surface (the surface opposite to the firstsubstrate 1 side) of the first electrode 3. The second binder 72 is madeof a silicone resin, and is disposed to fill in the space enclosed bythe second electrode 4, the layer made of the first binder 71, and themicrocapsules 5 in one pixel. That is, in a laminar material, aplurality of microcapsules 5 are arranged such that one microcapsule isdisposed in the thickness direction, and are fixed with the secondbinder 72. The laminar material is fixed to the first electrode 3 withthe first binder 71, and is fixed to the second electrode 4 with thesecond binder 72.

This first binder 71 corresponds to the “first component” constitutingthe fourth electrophoretic apparatus of the present invention, and thesecond binder 72 corresponds to the “second component” constituting thefourth electrophoretic apparatus of the present invention.

A display method of the electrophoretic display device of the presentembodiment will now be described with reference to FIG. 11. As shown inFIG. 11, this electrophoretic display device is composed of the panel10C shown in FIG. 10 and a driving circuit 20. The driving circuit 20 isprovided with a switch 21 and voltage sources 22 a and 22 b. The firstelectrode 3 of the panel 10C is connected to the switch 21, and thesecond electrode 4 is connected to one terminal of each of the voltagesources 22 a and 22 b.

As shown in FIG. 11(A), when the switch 21 is in the open position andno voltage is applied between the electrodes 3 and 4, theelectrophoretic particles 61 and 62 in the microcapsule 5 are uniformlydispersed in the liquid phase dispersion medium 63. Consequently, theliquid phase dispersion medium 63, in the condition in whichelectrophoretic particles 61 and 62 are uniformly dispersed, is observedfrom the first substrate (transparent substrate) 1 side. That is, thispixel becomes transparent (in a strict sense, light gray) in thiscondition.

Following this condition, as shown in FIG. 11(B), the switch 21 isconnected to the voltage source 22 a such that the second electrode 4becomes positive and the first electrode 3 becomes negative and,thereby, positively charged black electrophoretic particles 62 migratetoward the first electrode (transparent electrode) 3 side because thefirst electrode 3 has become a negative pole. Negatively charged whiteelectrophoretic particles 61 migrate toward the second electrode 4 sidebecause the second electrode 4 has become a positive pole. Consequently,the black electrophoretic particles 62 are observed from the firstsubstrate (transparent substrate) 1 side. That is, this pixel becomesblack in this condition.

Following this condition, as shown in FIG. 11(C), the switch 21 isswitched to the open position and no voltage is applied between theelectrodes 3 and 4 in the resulting condition. However, theelectrophoretic particles 62 remain adjacent the first electrode(transparent electrode) 3 side due to a Coulomb force between thenegative charge carried by the first electrode (transparent electrode) 3and the positive charge carried by the electrophoretic particles 62. Theelectrophoretic particles 61 remain adjacent the second electrode 4 sidedue to a Coulomb force between the positive charge carried by the secondelectrode 4 and the negative charge carried by the electrophoreticparticles 61. Consequently, the black electrophoretic particles 62 arestill observed from the first substrate (transparent substrate) 1 sideand, therefore, this pixel remains black.

Following this condition, as shown in FIG. 11(D), the switch 21 isconnected to the voltage source 22 b such that the first electrode 3becomes positive and the second electrode 4 becomes negative and,thereby, positively charged black electrophoretic particles 62 migratetoward the second electrode 4 side because the second electrode 4 hasbecome a negative pole. Negatively charged white electrophoreticparticles 61 migrate toward the first electrode (transparent electrode)3 side because the first electrode 3 has become a positive pole.Consequently, the white electrophoretic particles 61 are observed fromthe first substrate (transparent substrate) 1 side. That is, the pixelbecomes white in this condition.

Since the first binder 71 made of an acrylic resin has high chemicalaffinity for the electrophoretic particles 6 a made of titanium dioxideis formed into a laminar shape on the first electrode 3, and the secondbinder 72 made of a silicone resin has low chemical affinity therefor isused to fix between microcapsules 5 adjacent to each other, theelectrophoretic particles 62 can be adjacent the first electrode 3 sideand the electrophoretic particles 61 can be adjacent the secondelectrode 4 side for, for example, one month or more in the conditionshown in FIG. 11(C). When the switch 21 is changed from the conditionshown in FIG. 11(C) to the condition shown in FIG. 11(D), theelectrophoretic particles 62 instantaneously move to the secondelectrode 4 side and the electrophoretic particles 61 instantaneouslymove to the first electrode 3 side, in unison.

As such, when the application of a voltage is stopped after an image isdisplayed by application of the voltage, the displayed image can be heldfor a long time without disappearing. In addition, erasure of the imagecan be excellently performed immediately after the switching takesplace. That is, the electrophoretic display device of the presentembodiment is a microcapsule type electrophoretic apparatus having anexcellent memorization property and an excellent erasability.

In contrast, with respect to a panel which differs simply in that nolayer made of the first binder 71 is disposed, although theelectrophoretic particles 62 instantaneously move to the secondelectrode 4 side and the electrophoretic particles 61 instantaneouslymove to the first electrode 3 side when the switch 21 is changed fromthe condition shown in FIG. 11(C) to the condition shown in FIG. 11(D),the electrophoretic particles 62 can be adjacent the first electrode 3side and the electrophoretic particles 61 can be adjacent the secondelectrode 4 side only for about 10 minutes in the condition shown inFIG. 11(C).

With respect to a panel in which no layer made of the first binder 71 isdisposed and an acrylic resin is used as the second binder 72, althoughthe electrophoretic particles 62 can be adjacent the first electrode 3side and the electrophoretic particles 61 can be adjacent the secondelectrode 4 side for, for example, six months or more in the conditionshown in FIG. 11(C), when the switch 21 is changed from the conditionshown in FIG. 11(C) to the condition shown in FIG. 11(D), all of theelectrophoretic particles 62 do not instantaneously move to the secondelectrode 4 side in unison and all of the electrophoretic particles 61do not instantaneously move to the first electrode 3 side in unison and,therefore, it may be observed that white spots remain in a blackbackground in the resulting state.

An electrophoretic display device of the eighth embodiment will now bedescribed with reference to FIG. 12. The electrophoretic display deviceof the present embodiment is a partition type electrophoretic displaydevice. FIG. 12 is a sectional view of one pixel of an electrophoreticdisplay panel.

Since the electrophoretic display device of the present embodiment is apartition type, in contrast to the electrophoretic display device of themicrocapsule type in the seventh embodiment, an electrophoreticsuspension 60 composed of electrophoretic particles 61 and 62 and aliquid phase dispersion medium 63 is contained in a space divided bypartitions 8 between the first and second electrodes 3 and 4. Theconfiguration, other than this difference, is basically the same as thatin the third embodiment. That is, this electrophoretic display panel(hereafter abbreviated as “panel”) is provided with a first substrate 1and a second substrate 2 arranged to face each other, and a firstelectrode 3 and a second electrode 4 fixed to opposing surfaces of therespective substrates 1 and 2.

In this electrophoretic display device, a first layer 71 a made of anacrylic resin and a second layer 72 a made of a silicone resin areprovided between the layer made of the electrophoretic suspension 60 andthe first electrode (transparent electrode) 3, in that order, from thefirst electrode 3 side. This first layer 71 a corresponds to the “firstcomponent” constituting the third electrophoretic apparatus of thepresent invention, and the second layer 72 a corresponds to the “secondcomponent” constituting the fourth electrophoretic apparatus of thepresent invention.

In this device as well, the electrophoretic suspension 60 is composed ofwhite electrophoretic particles 61 made of titanium dioxide particles,black electrophoretic particles 62 made of acrylic resin particles, anda transparent liquid phase dispersion medium 63 made of dodecylbenzene.That is, electrophoretic particles composed of positively chargedparticles (acrylic resin particles) and negatively charged particles(titanium dioxide particles), which have colors different from eachother, are used in the present embodiment.

In this device, the first electrode 3, on the observation surface side,is connected to one terminal of each of the voltage sources 22 a and 22b, and the second electrode 4 is connected to the switch 21. In a mannersimilar to that in the first embodiment, the switch 21 is operated, theelectrophoretic particles 61 and 62 are moved to the first electrode 3side or the second electrode 4 side, and each pixel can be made white orblack.

According to the electrophoretic display device of the presentembodiment, since the first layer 71 a made of an acrylic resin has ahigh chemical affinity for the electrophoretic particles 61 made oftitanium dioxide, and the second layer 72 a made of a silicone resin hasa low chemical affinity therefor are provided between the layer made ofthe electrophoretic suspension 60 and the first electrode (transparentelectrode) 3, in that order, from the first electrode 3 side, when theapplication of a voltage is stopped after an image is displayed byapplication of the voltage, the displayed image can be held for a longtime without disappearing. In addition, erasure of the image can beexcellently performed immediately after the switching takes place. Thatis, the electrophoretic display device of the present embodiment is amicrocapsule type electrophoretic apparatus having an excellentmemorization property and an excellent erasability.

As constituent materials and the like for the electrophoretic apparatus,other than those materials used and described in the above-describedembodiments, a variety of materials can be used. The following areexemplifications thereof.

The first substrate 1 disposed on the observation side is essentially atransparent (having a light transmission property) substrate. Forexample, a resin film of polyethylene terephthalate (PET),polyethersulfone (PES) or the like, or a quartz substrate can be used inaddition to the transparent glass substrate. The second substrate 2 isnot necessarily a transparent substrate and, therefore, a metal plate orthe like can also be used therefor.

The first electrode 3 disposed on the observation side is essentially atransparent (having a light transmission property) electrode, and anIDIXO (In₂O₃—ZnO) thin film and the like can be used in addition to theITO thin film. As the second electrode 4, a thin film made of a metal,for example, gold (Au), platinum (Pt), silver (Ag), nickel (Ni),titanium (Ti) or chromium (Cr), can be used in addition to the aluminumthin film.

As the electrophoretic particles 6 a, colored particles capable of beingcharged in an insulating liquid phase dispersion medium are used. Forexample, white aluminum oxide (Al₂O₃) particles, particles made ofcolored synthetic resins (polyethylene resin, polystyrene resin oracrylic resin), those in which a metal film of aluminum, silver or thelike is formed on a synthetic resin can be used in addition to thetitanium dioxide (TiO₂) particles. Furthermore, preferably, particleswhich have been surface-treated with a surfactant, a dispersing agentand the like are used in order to suppress occurrence of coagulation andreduce to the specific gravity.

Examples of colorants for the electrophoretic particles 6 a include anyone of, or a mixture of at least two of black pigments. For example,aniline black and carbon black; white pigments such as zinc white andantimony trioxide; azo pigments such as monoazo, disazo and polyazo;yellow pigments such as isoindolinone, chrome yellow, yellow iron oxide,cadmium yellow, titanium yellow and antimony; red pigments such asquinacridone red and chrome vermilion; blue pigments, such as iron blue,ultramarine and cobalt blue; green pigments such as phthalocyaninegreen; phthalocyanine blue, indanthrene blue, anthraquinone dyes and thelike.

As necessary, a charge-controlling agent composed of particles of metalsoap, resin, rubber, oil, varnish, compound and the like; a dispersingagent such as a titanium-based coupling agent, an aluminum-basedcoupling agent or a silane-based coupling agent; an electrolyte, asurfactant, a lubricant, a stabilizer and the like may be added to theabove-described pigment.

As the liquid phase dispersion medium 6 b, an insulating liquid, forexample, a substantially water-insoluble organic solvent, is used inwhich the electrophoretic particles 6 a are likely to be charged, andthe charged state is stabilized. Examples of the above-describedsolvents include any one of long chain alcohol-based solvents such asdodecanol and undecanol; multicarbon ketones such as dibutyl ketone andmethyl isobutyl ketone; aliphatic hydrocarbons such as pentane, hexaneand octane; alicyclic hydrocarbons such as cyclohexane andmethylcyclohexane; aromatic hydrocarbons such as benzene, toluene,xylene, hexylbenzene, heptylbenzene, octylbenzene, nonylbenzene,decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene,tetradecylbenzene and other benzenes having a long chain alkyl group;halogenated hydrocarbons such as methylene chloride, chloroform, carbontetrachloride and 1,2-dichloroethane; and various oils such as siliconoil and olive oil, or a mixture thereof.

Preferably, those which are colored by dyes and which contain ionicsurfactants are used as the liquid phase dispersion media 6 b.

Examples of materials for capsule films of microcapsules 5 include amixture of a polycationic material such as gelatin, and a polyanionicmaterial such as gum Arabic, sodium alginate, carrageenan, carboxymethylcellulose, agar, polyvinylbenzenesulfonic acid and polyvinyl ethermaleic anhydride. Furthermore, examples thereof include formalinresorcinol resins, polyvinyl alcohols, polyurethane resins, acrylateresins, polymethyl-γ-methyl-L-glutamate, melamine, methacrylate resins,formaldehyde resins, polyvinyl pyrrolidone resins and fluorine resins.

Embodiments of Electronic Equipment

The electrophoretic apparatus of the present invention can be applied tothe display portions of various electronic equipment, for example,electronic papers, electronic notes, electronic book, mobile typepersonal computers, cellular phones and digital still cameras.

FIG. 14 is a perspective view showing an exterior configuration ofelectronic paper (rewritable sheet). This electronic paper 200 iscomposed of a main body 201 and an electrophoretic display panel 202.The main body 201 and the electrophoretic display panel 202 are formedinto the shape of a sheet having a paper-like feel and flexibility. Adriving circuit of the electrophoretic display panel 202 is built in themain body 201 or is provided as a rewriting device separate from theelectronic paper.

FIG. 15 is a sectional view (a) and a plan view (b) showing arewriting/display device of the above-described electronic paper 200.This device is provided with a housing 401, two transfer roller pairs402 a and 402 b, a rectangular hole 403 arranged in the observationsurface (display surface) of the housing 401, a transparent glass plate404 fitted into the rectangular hole 403, an insertion hole 405 forinserting into the housing 401 of the electronic paper 200, a socket407, a controller 408, and an operating portion 409.

The two transfer roller pairs 402 a and 402 b are arranged in theinterior of the housing 401 with a clearance therebetween. One transferroller pair 402 b is arranged in the proximity of an insertion hole 405of the electronic paper 200, and the other transfer roller pair 402 a isarranged at a position some distance from the insertion hole 405. Thesocket 407 is arranged in the side deeper (opposite to the insertionhole 405 side) than is the transfer roller pair 402 a at the positionsome distance from the insertion hole 405.

A terminal portion 205 is provided at the end of the electronic paper200. Both end portions of the electronic paper 200 inserted from theinsertion hole 405 into the housing 401 are held with the two transferroller pairs 402 a and 402 b. Under this condition, the terminal portion205 of the electronic paper 200 is inserted into the socket 407, and theother end in the opposite side extends off the insertion hole 405. Theelectronic paper 200 can be taken off from the housing 401 by holdingthis end portion, followed by drawing the paper 200 out. The socket 407is connected to the controller 408 provided with the driving circuit.The operating portion 409 is provided beside the transparent glass plate404 of the display surface of the housing 401.

When this device is used, the electronic paper 200 is put into thehousing 401 from the insertion hole 405 such that the display surface ofthe electronic paper 200 faces the transparent glass plate 404 side. Theoperating portion 409 is operated and, thereby, the controller 408 isactivated to write an image on the electronic paper 200, and to erase orrewrite a displayed image. With respect to the electronic paper 200 onwhich the image has been written, the image can be seen through thetransparent glass plate 404 while the electronic paper 200 is in thehousing 401, or the electronic paper 200 can be taken off from thehousing 401 and be carried.

FIG. 16 is a perspective view showing an exterior configuration of anelectronic note. In this electronic note, a plurality of theabove-described electronic paper 200 shown in FIG. 14 are bound, and acover 301 is provided on the outside thereof to take the shape of anotebook. When the cover 301 is provided with a display data inputdevice, the display content of the electronic paper 200 in a bound statecan be changed.

FIG. 17 is a perspective view showing an exterior configuration of anelectronic book. This electronic book 500 is provided with a main body501 composed of the electrophoretic display device and a cover 502. Themain body 501 is provided with a display portion 503 and an operatingportion 504. The cover 502 is attached to the main body 501 in order tobe opened or closed at will, and is configured such that the displaysurface of the display portion 503 and the operating portion 504 areexposed as the cover 502 is opened. A controller, a counter, a memory, adata reader for reading data in a storage medium such as a CDROM, andthe like are built in the main body 501.

FIG. 18 is a perspective view showing an exterior configuration of amobile type personal computer. This personal computer 600 includes amain body portion 602 provided with a keyboard 601, and a display unit603 composed of the electrophoretic display device.

FIG. 19 is a perspective view showing an exterior configuration of acellular phone. This cellular phone 700 is provided with a plurality ofoperation buttons 701 and, in addition, an earpiece 702, a mouthpiece703, and a display panel 704 composed of the electrophoretic displaydevice.

FIG. 20 is a perspective view showing the configuration of a digitalstill camera, and connection with external equipment is briefly shown.This digital still camera 800 is provided with a case 801, a displaypanel 802 which is formed on the back of the case 801 and which iscomposed of the electrophoretic display device performing display basedon image pickup signals from a CCD (Charge Coupled Device), and a lightreceiving unit 803 including an optical lens. The CCD and the like areformed in the observation side (in the drawing, back side) of the case801. A shutter button 804 and a circuit substrate 805, in which theimage pickup signal from the CCD at the point when this shutter button804 is pushed, is transferred and stored.

Video signal output terminals 806 and a data communication input-outputterminal 807 are provided on the side surface of the case 801 of thedigital still camera 800, and the former and the latter are connected toa television monitor 806A and a personal computer 807A, respectively, asnecessary. Subsequently, the image pickup signal stored in a memory ofthe circuit substrate 805 is output to the television monitor 806A orthe personal computer 807A through a predetermined operation.

In addition to them, examples of electronic equipment, to which theelectrophoretic display device can be applied as a display portion andthe like, include televisions, viewfinder type and monitor-direct-viewtype videotape recorders, car navigation devices, pagers, electronicnotepads, desk-top calculators, word processors, work stations,videophones, POS terminals, equipment provided with a touch panel, andthe like.

EXAMPLES Example 1

An electrophoretic display panel was prepared by the following method,and a manufacturing process of the microcapsules will be described withreference to FIG. 13.

As shown in FIG. 13(A), 5.5 g of a gelatin powder (manufactured by KantoKagaku), 5.5 g of a gum Arabic powder (manufactured by Kanto Kagaku),and 60 g of were put in a 500 ml-beaker to dissolve these powders intothe water.

As shown in FIG. 13(B), an electrophoretic suspension (preparedbeforehand) is dropped into the resulting solution while the solutionwas agitated at a rotation speed of 250 rpm. After the dropping wascompleted, the rotation speed was increased to 1,300 rpm, and agitationwas further performed for 1 hour.

This electrophoretic suspension was prepared by the following method. 50g of TiO₂ particles (electrophoretic particles) “CR-90” manufactured byISHIHARA SANGYO KAISHA, Ltd., 2.3 g of a titanate (titanic acidsalt)-based coupling agent “KR-TTS” manufactured by Ajinomoto Co., Inc.,1 g of an aluminum-based coupling agent “AL-M” manufactured by AjinomotoCo., Inc.:, and 300 g of dodecylbenzene (liquid phase dispersion medium)manufactured by Kanto Kagaku were put into a 500 ml-flask and agitatedwhile an ultrasonic vibration was applied.

In this manner, a suspension was prepared in which TiO₂ particles weredispersed in dodecylbenzene, while being positively charged. One hundredgrams of this suspension was taken out of this flask, and 1.8 g ofanthraquinone-based blue dye (manufactured by CHUO SYNTHETIC CHEMICALCO., LTD.) was dissolved into the suspension. In this manner, anelectrophoretic suspension was prepared, in which white TiO₂ particleswere dispersed in blue dodecylbenzene.

As shown in FIG. 13(C), 300 ml of warm water was added to theabove-described solution while the above-described solution was agitatedat a rotation speed of 500 rpm, followed by agitation for another 30minutes at the same rotation speed.

As shown in FIG. 13(D), 11 ml of 10% acetic acid solution was droppedinto the resulting solution. As shown in FIG. 13(E), agitation wasperformed for another 2 hours at a rotation speed of 500 rpm while thewhole solution was kept at 0° C. by cooling from the outside of thebeaker.

As shown in FIG. 13(F), 2.7 ml of formalin solution (manufactured byKanto Kagaku) was added to the resulting solution. Furthermore, as shownin FIG. 13(G), 22 ml of 10% sodium carbonate solution was added to theresulting solution.

As shown in FIG. 13(H), the cooling was stopped, and the temperature ofthe whole solution was returned to room temperature, followed by furtheragitation at the same rotation speed. This agitation was performed forone night and, thereby, a microcapsule suspension in which microcapsuleswere dispersed in water was prepared, as shown in FIG. 13(I). Thecapsule film of this microcapsule is composed of a mixture of gelatinand gum Arabic at a ratio of 1:1, and an electrophoretic suspension(white TiO₂ particles+blue dodecylbenzene) is contained in this capsulefilm.

Microcapsules having particle diameters of 40 to 60 μm were taken out ofthe microcapsule suspension. Microcapsules having particle diameterslarger than the above-described range were removed with a sieve, andmicrocapsules having particle diameters smaller than the above-describedrange were removed by a method using a separatory funnel.

The thus prepared microcapsules, a silicone binder “POLON-MF-40”manufactured by Shin-Etsu Chemical Co., Ltd., and an acrylic binder“E272” manufactured by Mitsui Toatsu Chemicals, Inc., were mixed suchthat a final weight ratio after drying of microcapsule:siliconeresin:acrylic resin=10:1:1 was achieved. The resulting mixture wasapplied by coating to a PET film provided with pixel electrodes made ofITO (an ITO thin film patterned into the shape of pixels) to achieve afilm thickness of 150 μm, followed by drying at 90° C. for 20 minutes.In this manner, a layer composed of microcapsules 5 and a binder 7 wasformed on the surface of the PET film provided with the pixelelectrodes.

A PET film provided with an ITO thin film all over the surface thereofwas put on the above-described layer of the resulting PET film while theITO thin film side was faced toward the above-described layer side,followed by laminating with a laminator. In this manner, anelectrophoretic display panel was prepared, in which one pixel had thestructure shown in FIG. 1. Here, the condition of lamination with thelaminator was adjusted and, thereby, the spacing between the ITOs of thetwo PET films became slightly larger than the maximum diameter of themicrocapsules, so that only one microcapsule was disposed in the panelthickness direction.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from white to blueoccurred instantaneously with no occurrence of unevenness.

Example 2

Microcapsules prepared by the same method as that in Example 1 (exceptthat the composition of the capsule film was changed to gelatin: gumArabic=3:2), the silicone binder “POLON-MF-40” manufactured by Shin-EtsuChemical Co., Ltd., and the acrylic binder “E272” manufactured by MitsuiToatsu Chemicals, Inc., were mixed such that a final weight ratio afterdrying of microcapsule:silicone resin:acrylic resin=10:0.8:1.2 wasachieved.

The resulting mixture was applied by coating to a PET film provided withpixel electrodes made of ITO (an ITO thin film patterned into the shapeof pixels) to achieve a film thickness of 130 μm, followed by drying at90° C. for 20 minutes. In this manner, a layer composed of microcapsules5 and a binder 7 was formed on the surface of the PET film provided withthe pixel electrodes.

The steps following this were performed by the same method as that inExample 1, so that an electrophoretic display panel 10 was prepared, inwhich one pixel had the structure shown in FIG. 1.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from white to blueoccurred instantaneously with no occurrence of unevenness.

Example 3

An electrophoretic display panel was prepared by the same method as thatin Example 1 except that an electrophoretic suspension was prepared bythe following method.

The electrophoretic suspension was prepared by the following method. 50g of TiO₂ particles (electrophoretic particles) “CR-90” manufactured byISHIHARA SANGYO KAISHA, Ltd., 50 g of black acrylic resin particles(electrophoretic particles) manufactured by Soken Chemical andEngineering Co., Ltd., 2.3 g of a titanate (titanic acid salt)-basedcoupling agent “KR-TTS” manufactured by Ajinomoto Co., Inc., 1 g of analuminum-based coupling agent “AL-M” manufactured by Ajinomoto Co.,Inc., and 300 g of dodecylbenzene (liquid phase dispersion medium)manufactured by Kanto Kagaku were put into a 500 ml-flask, followed byagitation while ultrasonic vibration was applied.

In this manner, an electrophoretic suspension was prepared, in whichwhite TiO₂ particles were dispersed in dodecylbenzene, while beingnegatively charged, and the black acrylic resin particles were dispersedin dodecylbenzene, while being positively charged. As shown in FIG.13(B), the resulting electrophoretic suspension was dropped into asolution of a gelatin powder and a gum Arabic powder while the solutionwas agitated at a rotation speed of 250 rpm.

The steps other than this were performed by the same method as that inExample 1, so that an electrophoretic display panel 10A was prepared, inwhich one pixel had the structure shown in FIG. 4.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from white to blackoccurred instantaneously with no occurrence of unevenness.

Example 4

An electrophoretic display panel was prepared by the following method.

Microcapsules were prepared by the same method as that in Example 1. Theresulting microcapsules and a silicone binder “POLON-MF-40” manufacturedby Shin-Etsu Chemical Co., Ltd., were mixed such that a final weightratio after drying of microcapsule:silicone resin=5:1 was achieved. Apaste composed of the resulting mixture was applied by coating to a PETfilm provided with pixel electrodes made of ITO (an ITO thin filmpatterned into the shape of pixels) to achieve a film thickness of 150μm, followed by keeping at 90° C. for 30 minutes.

In this manner, most of the water was removed from the paste coatingfilm. An acrylic binder “E272” manufactured by Mitsui Toatsu Chemicals,Inc., was applied thereto by coating to achieve a predeterminedthickness (a thickness corresponding to a thickness after drying of 1μm), followed by drying at 90° C. for 20 minutes. In this manner, alayer composed of the microcapsules and the silicone resin (firstbinder) and a layer composed of the acrylic resin (second binder) wereformed in that order on the surface of the PET film provided with thepixel electrodes. When the acrylic binder is applied by coating onto thelayer composed of the microcapsules and the silicone resin, the acrylicbinder may diffuse into the silicone resin in the above-described layer.

A PET film provided with an ITO thin film all over the surface thereofwas put on the layer composed of the acrylic resin of the resulting PETfilm while the ITO thin film side was faced toward the above-describedlayer side, followed by laminating with a laminator. In this manner, anelectrophoretic display panel 10B was prepared, in which one pixel hadthe structure shown in FIG. 7. Here, the condition of lamination withthe laminator was adjusted and, thereby, the spacing between the pixelelectrode of one PET film and the layer composed of the acrylic resin ofthe other PET film became slightly larger than the maximum diameter ofthe microcapsules, so that only one microcapsule was disposed in thepanel thickness direction.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from white to blueoccurred instantaneously with no occurrence of unevenness.

Example 5

An electrophoretic display panel 10B in which one pixel had thestructure shown in FIG. 7 was prepared by the same method as that inExample 4 except that the composition of the capsule film was adjustedin order that the ratio of gelatin:gum Arabic=3:2 was achieved inpreparation of microcapsules.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from white to blueoccurred instantaneously with no occurrence of unevenness.

Example 6

An electrophoretic display panel was prepared by the same method as thatin Example 4 except that an electrophoretic suspension was prepared bythe following method.

The electrophoretic suspension was prepared by the following method. 50g of TiO₂ particles (electrophoretic particles) “CR-90” manufactured byISHIHARA SANGYO KAISHA, Ltd., 50 g of black acrylic resin particles(electrophoretic particles) manufactured by Soken Chemical andEngineering Co., Ltd., 2.3 g of a titanate (titanic acid salt)-basedcoupling agent “KR-TTS” manufactured by Ajinomoto Co., Inc., 1 g of analuminum-based coupling agent “AL-M” manufactured by Ajinomoto Co.,Inc., and 300 g of dodecylbenzene (liquid phase dispersion medium)manufactured by Kanto Kagaku were put into a 500 ml-flask, followed byagitation while ultrasonic vibration was applied.

In this manner, an electrophoretic suspension was prepared, in whichwhite TiO₂ particles were dispersed in dodecylbenzene while beingnegatively charged and the black acrylic resin particles were dispersedin dodecylbenzene while being positively charged. As shown in FIG.13(B), the resulting electrophoretic suspension was dropped into asolution of a gelatin powder and a gum Arabic powder while the solutionwas agitated at a rotation speed of 250 rpm.

The steps other than this were performed by the same method as that inExample 4, so that an electrophoretic display panel 10C was prepared, inwhich one pixel had the structure shown in FIG. 10.

The resulting panel was connected to a driving circuit, and a drivingtest was performed. As a result, the display image holding time was onemonth or more, and in erasure, the change in color from black to whiteoccurred instantaneously with no occurrence of unevenness.

1. An electrophoretic apparatus comprising a first electrode, a secondelectrode and a plurality of closed spaces divided by partitions,wherein the closed space contains an electrophoretic suspension in whichelectrophoretic particles are dispersed in a dispersion medium, and theelectrophoretic particles migrate by application of a voltage via thefirst electrode and the second electrode, wherein a component isdisposed between the closed space and at least one of the firstelectrode and the second electrode, wherein the component comprises amixture including at least two different materials of a first materialand a second material, wherein the first material and the secondmaterial have different holding powers for holding the unevendistribution state of the electrophoretic particles without applying anyvoltage, the uneven distribution state being caused by the applicationof a voltage, and wherein the holding power of the first material ishigher than that of the second material.
 2. The electrophoreticapparatus according to claim 1, wherein the affinity of the firstmaterial for the electrophoretic particles is higher than the affinityof the second material for the electrophoretic particles.
 3. Theelectrophoretic apparatus according to claim 1, wherein the polarity ofthe first material is higher than the polarity of the second material.4. The electrophoretic apparatus according to claim 1, wherein theelectrophoretic particles are titanium dioxide (TiO₂) particles, whereinthe first material is an acrylic resin, and wherein the second materialis a silicone resin.
 5. The electrophoretic apparatus according to claim1, wherein the electrophoretic particles comprise positively chargedparticles and negatively charged particles which have colors differentfrom each other.
 6. The electrophoretic apparatus according to claim 1,wherein the electrophoretic particles comprise titanium dioxide (TiO₂)particles and colored particles made of an acrylic resin, wherein thefirst material is an acrylic resin, and wherein the second material is asilicone resin.